Last week Symantec released an update for its antivirus software that had an unintended consequence, causing some Windows XP machines to receive the dreaded Blue Screen of Death. The defective update was live for around eight hours between July 11th and 12th, and this weekend Symantec finally got to the root of the problem, explaining that the error was limited to XP machines running the latest version of the company's SONAR technology, the updated July 11th signature set, and "certain third-party software" — though it's not clear just what that software is.

According to the company, an incompatibility issue with the unnamed software was missed during testing, and is the cause of the blue screens. "The compatibility testing part of the quality assurance process for SONAR signatures missed catching this compatibility issue," Symantec's Orla Cox wrote. "It is this part of our process that we will be improving to avoid future issues." If you're the owner of an affected machine, the company has posted a workaround that should remedy the issue.